1. Field of the Invention
This invention relates to frequency shift keying (FSK) modems and in particular to integrated circuit FSK modems employing field effect transistors and switched capacitor filters.
2. Description of the Prior Art
Discreet components type FSK modems are well-known in the prior art.
As integrated circuits became commonplace, digital processing to both form and receive FSK signals was introduced. For example, see U.S. Pat. No. 4,142,245 "Multi-Frequency Digital Waves Synthesizer For Providing Analog Output Signals" assigned to the assignee of this invention.
Other digital circuits are known in the prior art, some of which are referred to as single chip modems. However, to properly employ such prior art single chip modems, it is necessary to provide external filters and limiters.
The FSK modem of this invention provides all of the modulation, demodulation, and filtering functions on a single chip. The analog functions of the circuit are implemented using switched capacitor technology.